ZnO nanoparticle coated exfoliated graphite composite, method of producing composite and use in Li-ion battery

Abstract

Composites comprising an exfoliated graphite support material having a degree of graphitization g in an range of 50 to 93%, obtained by XRD Rietveld analysis, which is coated with ZnO nanoparticles. These composites are produced by three different methods: A) (syn) the method comprises the following consecutive steps: i) a Zn(II)salt is dissolved in a solvent ii) graphite and a base are added simultaneously iii) the mixture is stirred under impact of ultrasound iv) the solvent is removed from the suspension or B) (pre) the method comprises the following consecutive steps: i) graphite is suspended in a solvent and exfoliated via impact of ultrasound ii) a Zn(II)salt and a base are added simultaneously forming nano-ZnO particles iii) the mixture is stirred iv) the solvent is removed from the suspension or C) (post) the method comprises the following steps: i) a Zn(II)salt and a base are mixed in a solvent in a first reactor forming nano-ZnO particles ii) graphite is exfoliated via impact of ultrasound in a second reactor iii) both suspensions of i) and ii) are mixed together iv) after step iii) the solvent is removed from the suspension. These coated composites may be tempered in a further step and again coated and again tempered.

The invention claimed is: 
     
       1. Composite comprising an exfoliated graphite support material having a degree of graphitization g in a range of 50 to 93%, obtained by XRD Rietveld analysis, wherein g is determined by the formula (IV): 
       
         
           
             
               
                 
                   
                     g 
                     = 
                     
                       
                         
                           d 
                           ng 
                         
                         - 
                         
                           d 
                           
                             0 
                             ⁢ 
                             0 
                             ⁢ 
                             2 
                           
                         
                       
                       
                         
                           d 
                           ng 
                         
                         - 
                         
                           d 
                           g 
                         
                       
                     
                   
                 
                 
                   
                     ( 
                     IV 
                     ) 
                   
                 
               
             
           
         
         wherein d 002  is the distance of the lattice planes determined of the measured position of the (002) reflex and calculated according to the Bragg equation, d g =335.4 pm which is a literature value for totally graphitized carbon and d ng  represents non-graphitized carbon with a value of 344 pm, 
         wherein said exfoliated graphite support material is coated with ZnO nanoparticles. 
       
     
     
       2. Composite according to  claim 1 , wherein the composite has a content of exfoliated graphite and ZnO in a range of 85 to 100 wt.-%, based on the total weight of the composite. 
     
     
       3. Composite according to  claim 1 , wherein the specific content c sp,ZnO  of the ZnO nanoparticles, determined from the formula (V):
     c   sp,ZnO   =m   ZnO/βgr   (V)
 
 wherein m ZnO  is the content of ZnO in wt.-%, based on the mass of the total composite as determined from ICP-OES and β gr  is the specific surface determined by BET of the exfoliated graphite support material, is in a range of 0.2 to 0.85 wt-% g/m 2 . 
 
     
     
       4. Composite according to  claim 3 , wherein the composite is a primarily tempered composite b) and has a specific content c sp,ZnO  of the ZnO nanoparticles, determined from the formula (V):
     c   sp,ZnO   =m   ZnO /β gr   (V)
 
 wherein m ZnO  is the content of ZnO in wt.-%, based on the mass of the total composite as determined from ICP and β gr  is the specific surface determined by BET of the exfoliated graphite support material, is in a range of 0.2 to 0.45 wt-% g/m 2 . 
 
     
     
       5. Composite according to  claim 1 , wherein the exfoliated graphite material is a non-oxidized graphite. 
     
     
       6. Composite according to  claim 1 , wherein any of the two basic components exfoliated graphite or ZnO nanoparticles of the composite are not formed on a further support material. 
     
     
       7. Composite according to  claim 1 , wherein the composites consist of
 a) primary composites, wherein the primary composite is produced by a first coating step of the exfoliated graphite support with ZnO nanoparticles; 
 b) primary tempered composites, which are obtained by tempering the primary composites a) in an inert or a reducing gas atmosphere at a temperature of 350 to 750° C.; 
 c) secondary composites, obtained by further coating of the primary tempered composites b) with ZnO nanoparticles; or 
 d) secondary tempered composites, which are obtained by tempering the secondary composites c) in an inert or a reducing atmosphere at a temperature of 350 to 750° C. 
 
     
     
       8. Composite according to  claim 7 , wherein the composites consist of
 a) primarily composites, wherein the primary composite is produced by a first coating step of the exfoliated graphite support with ZnO nanoparticles or 
 b) primarily tempered composites, which are obtained by tempering the primary composites a) in an inert or a reducing atmosphere, wherein the temperature of tempering is in a range of 420° C. to 750° C. when using an inert atmosphere or in a range of 375° C. to 700° C. when using a reducing atmosphere. 
 
     
     
       9. Composite according to  claim 7 , wherein at least one tempering step is made in a reducing atmosphere. 
     
     
       10. Composite according to  claim 7 , wherein the average particle size d 1,ZnO  of the ZnO nanoparticles in the primary coated composite a) is in a range from 3.0 to 7.0 nm as determined by TEM. 
     
     
       11. Composite according to  claim 7 , wherein the composite is a primary composite a) or a primary tempered composite b) and the ZnO nanoparticles have a surface coverage θ pr , determined from the equation (VII): 
       
         
           
             
               
                 
                   
                     
                       θ 
                       pr 
                     
                     = 
                     
                       
                         3 
                         2 
                       
                       × 
                       
                         c 
                         
                           1 
                           - 
                           c 
                         
                       
                       × 
                       
                         1 
                         
                           
                             ρ 
                             ZnO 
                           
                           ⁢ 
                           
                             r 
                             pr 
                           
                           ⁢ 
                           
                             β 
                             
                               E 
                               ⁢ 
                               G 
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     ( 
                     VII 
                     ) 
                   
                 
               
             
           
         
         wherein c is the mass quotient of the mass of ZnO to the sum of the masses of ZnO and exfoliated graphite, r pr  is the mean radius of the ZnO primary particles as determined by TEM, ρ ZnO  is the density of the ZnO nanoparticles, β EG  is the specific surface (BET) of the support material which is exfoliated graphite and wherein θ pr  is in a range of 21 to 54% for primary composites a) 
         or θ pr  is in a range of 2.5 to 38% for primary tempered composites b). 
       
     
     
       12. Composite according to  claim 7 ,
 wherein the composite is a primary coated composite a) and the TC's derived from the intensities of the XRD reflexes according to the ZnO nanoparticles exhibit TC(100)>0.9, TC(002)>1.1 and TC(100)/TC(002)<1, 
 or the composite is a primary coated tempered composite b) and the TC's derived from the intensities of the XRD reflexes according to the ZnO nanoparticles exhibit TC(100)>1, TC(002)>0.9 and the ratio TC(100)/TC(002) is in a range of 0.8 to 1.3. 
 
     
     
       13. Composite according to  claim 7 , wherein the average particle size d 1,ZnO  of the ZnO nanoparticles in the primary coated tempered composite b) which was tempered in an inert atmosphere is in a range from 10 to 100 nm as determined by TEM. 
     
     
       14. Composite according to  claim 7 , wherein the primarily coated tempered composite b) is tempered in reduced atmosphere and the average particle size d 1,ZnO  of the ZnO nanoparticles is in a range from 7 to 50 nm as determined by TEM. 
     
     
       15. Composite according to  claim 7 , wherein the composite is a primarily tempered composite b) and has a Zn-content of 52 to 58 atom-% as determined with EDX on cross sections of the composite and measured on single ZnO particles and referenced to Zn— and oxygen content only. 
     
     
       16. Composite according to  claim 7 , wherein the content of the ZnO nanoparticles is from 3 to 15 wt.-% for the primary coated composites a) and b), based on the total weight of the composite. 
     
     
       17. A method of producing a primary coated composite a) according to  claim 7  wherein
 A) (syn) the method comprises the following consecutive steps:
 i) a Zn(II)salt is dissolved in a solvent 
 ii) graphite and a base are added simultaneously 
 iii) the mixture is stirred under impact of ultrasound 
 iv) the solvent is removed from the suspension 
 or 
 
 B) (pre) the method comprises the following consecutive steps:
 i) graphite is suspended in a solvent and exfoliated via impact of ultrasound 
 ii) a Zn(II)salt and a base are added simultaneously forming nano-ZnO particles 
 iii) the mixture is stirred 
 iv) the solvent is removed from the suspension 
 or 
 
 C) (post) the method comprises the following steps:
 i) a Zn(II)salt and a base are mixed in a solvent in a first reactor forming nano-ZnO particles 
 ii) graphite is exfoliated via impact of ultrasound in a second reactor 
 iii) both suspensions of i) and ii) are mixed together 
 iv) after step iii) the solvent is removed from the suspension. 
 
 
     
     
       18. Method of producing a primary tempered composite b) according to  claim 7 , the method comprising:
 producing a primary coated composite a) by the method A), B), or C):
 A) (syn) the method comprises the following consecutive steps:
 i) a Zn(II)salt is dissolved in a solvent 
 ii) graphite and a base are added simultaneously 
 iii) the mixture is stirred under impact of ultrasound 
 iv) the solvent is removed from the suspension 
 or 
 
 B) (pre) the method comprises the following consecutive steps:
 i) graphite is suspended in a solvent and exfoliated via impact of ultrasound 
 ii) a Zn(II)salt and a base are added simultaneously forming nano-ZnO particles 
 iii) the mixture is stirred 
 iv) the solvent is removed from the suspension 
 or 
 
 C) (post) the method comprises the following steps:
 i) a Zn(II)salt and a base are mixed in a solvent in a first reactor forming nano-ZnO particles 
 ii) graphite is exfoliated via impact of ultrasound in a second reactor 
 iii) both suspensions of i) and ii) are mixed together 
 iv) after step iii) the solvent is removed from the suspension, and 
 
 tempering the primary coated composite a) at a temperature in a range of 420° C. to 750° C. in an inert atmosphere or at a temperature in a range of 375° C. to 700° C. in a reducing atmosphere. 
 
 
     
     
       19. Method of producing a primary tempered composite b) according to  claim 18 , wherein for composites tempered in an inert atmosphere the temperature of tempering is in a range of 550 to 730° C. and for composites tempered in a reducing atmosphere the temperature of tempering is in a range of 375 to 550° C. 
     
     
       20. Method of producing a primary tempered composite b) according to  claim 18 , wherein the reducing atmosphere consists essentially of a mixture of inert and reducing gases and is taken from the group consisting of N 2 /H 2  or Ar/H 2  mixtures or mixtures thereof. 
     
     
       21. Anode usable in a lithium-ion battery comprising the primary coated tempered composites b) or of secondary coated composite d) tempered in reduced atmosphere according to  claim 7 . 
     
     
       22. Lithium-ion battery comprising the anode of  claim 21 .